Electronically controlled fuel injectors typically inject fuel into a specific engine cylinder as a function of a fuel injection signal received from an electronic controller and are well known in the art. An example of a hydraulically actuated electronically controlled unit injector fuel system using hydraulically actuated electronically controlled unit injectors (hereinafter referred to a "HEUI injectors") is shown in U.S. Pat. No. 5,191,867 issued to Glassey on Mar. 9, 1993.
Emission regulations pertaining to engine exhaust emissions are increasingly becoming more restrictive throughout the world, including, for example, restrictions on emission of particulates and NO.sub.x. To control the power and emissions output of an internal combustion engine precisely, it is necessary to consistently control the timing and quantity of fuel injected into the engine cylinders. This requires utilizing different fuel injection rate waveform types in order to achieve optimum engine operation and emissions control. Further, tailoring the injection event, including sub-event(s), with respect to the total quantity of fuel delivered to a combustion chamber, injection rate of fuel delivered, portioning of fuel delivered and timing of such aspects of a fuel injection event, is one way in which to meet emission regulations. Therefore, at different engine operating conditions it may be necessary to control particular aspects of a fuel injection event differently.
In the past, hydraulically-actuated electronically-controlled fuel injection systems have included some mechanical limitations on the ability to consistently control aspects of the injection event and consistently provide a variety of achievable fuel injection rate waveform types. In some systems the injectors utilized have also been somewhat limited as to the fuel injection signal current waveform which could be utilized. Resulting problems included variations in the rate of injection like injecting fuel too rapidly within a given injection event, allowing fuel to be injected too soon or beyond a desired stopping point, variations in the pressure of the fuel being injected and variations in the dispersion of the fuel throughout the combustion chamber. Such problems can adversely affect emission outputs and fuel economy.
The present invention is directed to overcoming one or more of the problems as set forth above.